But a “hard” two-thirds vote — 21 of the 31 senators — is needed to approve a proposed constitutional amendment. Since there are 12 Democrats in the chamber, Republicans will need the support of at least two of them for the transportation proposal But most of the Democrats are opposed to the abortion measures, so there’s a chance of extracting concessions for their vote on transportation.

Of course, that depends on how things play out among the Democrats. Sen. Eddie Lucio, D-Brownsville, is voting for the abortion measures, so there’s no reason for him to vote against transportation on that front. Sen. Judith Zaffirini, D-Laredo, voted for one of the abortion measures in committee, but against the rest, so I want to ask her what she plans to do. Other Democrats may have reasons for supporting the transportation measure.

Sen. Kirk Watson of Austin, who heads the Senate Democratic Caucus, said some senators are determined to use whatever tools they have “to try to stop this assault on women.”

While Republicans generally support the anti-abortion measures, some have expressed concern about various proposals, which include a ban on abortion at 20 weeks, increased regulations for abortion facilities, requiring doctors who perform abortions to have admitting privileges at a hospital within 30 miles and new requirements for administering drugs that cause abortions. The provisions are wrapped into one omnibus bill, and there are separate bills on each.

There was also a math problem for Democrats who oppose the proposed new abortion regulations, related to procedural rules and Tuesday attendance. The transportation measure is ahead of the abortion legislation on the “regular order of business” agenda for the Senate, meaning a two-thirds vote would have been required to take up the abortion measures first and bypass the transportation. But this two-thirds requirement isn’t a hard two-thirds — it’s a two-thirds of those present. And not all the Democrats are present now.

It may all get worked out, but the delay shows the difficulty for Republicans who thought they could discount Democrats by virtue of special-session rules, which don’t require a two-thirds vote to take up all legislation.

The Senate just took up the transportation measure, Senate Joint Resolution 2, but Lt. Gov. David Dewhurst said only a preliminary vote will be taken, and then senators will recess until later in the day.